1. Field of the Invention
The present invention relates to a process for producing spherical metal particles and more specifically to an improved process for producing metal particles by spraying a molten metal within a chamber filled with a refrigerant gas using a centrifugal atomizer.
2. Description of the Prior Art
There have conventionally been well-known a process for producing metal particles which comprises the step of spraying a molten metal in a chamber filled with a refrigerant gas using a centrifugal atomizer to cool and solidify the scattered droplets and to thus form metal particles. In this production process, however, the scattered droplets formed by spraying a molten metal in a chamber filled with a refrigerant gas through a centrifugal atomizer should be cooled by the refrigerant gas atmosphere and should completely be solidified till the scattered droplets arrive at the inner wall of the chamber. If the scattered droplets collide with the inner wall of the chamber while they are still in an insufficiently solidified state, the resulting metal particles are adhered to one another and/or they undergo deformation and are correspondingly irregular in shape. For this reason, it has been difficult to obtain spherical metal particles having a uniform diameter. In order to eliminate the foregoing drawback, it is necessary to increase the flying time of the scattered droplets of a sprayed molten metal so that the scattered droplets are completely solidified and it is accordingly necessary to increase the scattering distance thereof. This correspondingly requires the use of an extremely large-sized chamber.
Incidentally, there has been disclosed, in Japanese Examined Patent Publication No. Sho 59-14084, a proposal capable of miniaturization of the chamber by controlling the time required till the scattered droplets of a molten metal are completely solidified through the use of a mixture which comprises at least two inert gases as the refrigerant gas to be used in the chamber. However, the control of the time required for the solidification to a preferred level according to the proposed process requires the use of a large quantity of helium gas which is excellent in heat transfer properties, but is very expensive. Therefore, such a proposed process is suitable for producing metal particles in a laboratory scale, i.e., in a small amount, but it is inevitable that the production of such metal particles in an industrial scale is quite unfavorable in the production cost.